[v2] unable to use theme-classic without remark-admonitions

🐛 Bug Report

Due to https://github.com/facebook/docusaurus/blob/master/packages/docusaurus-theme-classic/src/index.js#L56, you are unable to to use the @docusaurus/theme-classic theme without installing the remark-admonitions module. This shouldn’t be a hard requirement.

Have you read the Contributing Guidelines on issues?

Yep

To Reproduce

1. Create a V2 project with the following config

'use strict';

module.exports = {
  title: 'gulp.js',
  favicon: 'img/favicon.png',
  url: 'https://gulpjs.com/',
  baseUrl: '/',
  tagline: 'The streaming build system',
  // Used by the deployment
  organizationName: 'gulpjs',
  projectName: 'gulpjs.github.io',
  // The theme
  themeConfig: {},
  themes: ['@docusaurus/theme-classic'],
  plugins: [
    ['@docusaurus/plugin-content-docs', {
      path: '../converted-docs'
    }]
  ]
};

1. Try to run the project
2. See this error message

Expected behavior

The theme should be usable without external dependencies unless I opt-in.

Actual Behavior

Doesn’t compile and is unusable without installing the remark-admonitions module.

Your Environment

• Docusaurus version used: ^2.0.0-alpha.50
• Environment name and version (e.g. Chrome 78.0.3904.108, Node.js 10.17.0): 10.15.1
• Operating system and version (desktop or mobile): desktop

Reproducible Demo

None currently because I’m trying to upgrade the gulp website…

[phated]

@lex111 is there a reason that remark-admonitions isn’t just providing that lifecycle hook for itself?

[lex111]

@phated we really love the feedback from our users, thank you for that. We welcome any feedback, because we are still in the alpha stage.

I tend to include admonitions in every plugin (both for docs and blogs), instead of doing this in a preset. I think it was a predictable behavior.

BTW consider adding your project to our showcase at https://v2.docusaurus.io/showcase 😇